1. Field of the Invention
The present invention relates to a process for separating a cobalt component from a hydroesterification reaction mixture. More particularly, it relates to a process for separating a cobalt component from a reaction mixture obtained by a reaction of a polyhydric alcohol with an olefin and carbon monoxide in the presence of a cobalt carbonyl complex and a pyridine base, thereby separating a fatty acid ester of a polyhydric alcohol in high efficiency.
2. Description of the Prior Arts
The principle process for producing fatty acid esters of polyhydric alcohols has recently changed from the conventional process employing natural fatty acids as starting materials to a total synthesis.
The process for producing fatty acid esters of polyhydric alcohol by reacting a polyhydric alcohol with an olefin and carbon monoxide in the presence of a cobalt carbonyl complex and a pyridine base such as pyridine, vinyl pyridines and alkyl pyridines has been disclosed in Japanese Examined Patent Publication Nos. 39810/1977 and 31128/1978. By this process, fatty acid esters of polyhydric alcohols can be obtained by mass production with lower cost compared to the conventional process. However it is indispensible to recover and reuse the catalyst metal in order to employ a homogeneous catalytic reaction as an industrial process.
The following processes have been proposed as processes for recovering the cobalt component from the reaction mixture obtained by the hydroesterification reaction using a cobalt carbonyl complex.
A liquid hydrocarbon is added to the reaction mixture obtained by the hydroesterification reaction using an excess of an alcohol, thereby separating a hydrocarbon phase containing the ester from an alcohol phase containing the cobalt carbonyl complex (Japanese Examined Patent Publication No. 47676/1976, U.S. Pat. No. 3,856,832).
A lower alcohol is added to the hydroesterification reaction mixture thereby extracting most of the cobalt carbonyl complex into a lower alcohol phase (Japanese Unexamined Patent Publication No. 62192/1977).
The hydroesterification reaction is carried out in a liquid paraffin having high boiling point and the reaction mixture is separated into a paraffin phase containing the ester and a phase containing the cobalt carbonyl complex. The ester is separated from the paraffin phase by distillation, and the phase containing the cobalt carbonyl complex is recycled into the reaction system in a continuous hydroesterification reaction (Japanese Examined Patent Publication No. 37327/1978).
However, all of these known processes have disadvantages. The first process can not be employed in the process for producing the full ester of a polyhydric alcohol since that would require excess of the olefin.
The second process has the disadvantage that a large quantity of the ester would be recycled together with the catalyst because the ester reaction product is partitioned at about same ratio between the two phases.
The third process has the advantage of recycling the catalyst in high efficiency but has the disadvantage of requiring larger equipment such as a reactor, a separator and a distillation tower, which cause a high fixed cost because a large quantity of paraffin is used as a solvent.
The inventors have developed a process for recovering the cobalt component and for separating and purifying a fatty acid ester of a polyhydric alcohol in an industrially advantageous manners in the process for producing the fatty acid ester of a polyhydric alcohol by the hydroesterification reaction using cobalt carbonyl complex as a catalyst. As a result, the process of the present invention has been accomplished.